Cellulose filter papers derived separator featuring effective ion transferring channels for sodium-ion batteries

As a basic component of batteries, separators are proposed to apart the two electrodes while allowing the transport of ionic charge carriers. Cellulose separators have attracted tremendous attention due to their excellent thermal stability and wettability. In this study, we prepare all-cellulose composite (ACC) separators coated with Zn5(OH)8Cl2·H2O (ZHC) particles. The surface of the cellulose filter paper is partially dissolved by the 65% ZnCl2 solution, forming a tortuous and porous all-cellulose composite membrane. At the same time, ZHC is generated in situ on the surface during the removal of residual ZnCl2 from the cellulose, which effectively promotes the passage of a sodium ion (Na+) and substantially improves the cycling performance of the batteries. Density functional theory (DFT) calculations demonstrate that suitable adsorption energy on ZHC is favorable for promoting Na+ transport. The corresponding ACC separator exhibits high ionic conductivity (2.75 mS/cm) and Na+ transference number (0.82), correspondingly the assembled Na/hard carbon half-cells show an excellent reversible specific capacity (315 mA h/g at 25 mA/g) and cycling stability (the retention is 97.77% after 50 cycles at 50 mA/g), outperforming the glass fiber separator in both sodium-ion half-cell and full-cell.